Electron beam source assemblies for use in high pressure differential/vacuum environments are known in the prior art. Such assemblies generally include a thermionic emitter mechanism to generate and accelerate an electron beam which is deflected by a magnetic field into a crucible structure containing one or more materials. The material or materials are vaporized by the electron beam and deposited on the desired substrate. The vaporized material(s) is deposited on a desired substrate in, for example, the field of thin film deposition. One particular application is optical coatings. One such electron beam source assembly is disclosed in U.S. Pat. No. 3,883,679 to Shrader et al.; another is shown is U.S. Pat. No. 5,418,348, assigned to the assignee of the present invention.
The electron beam source assemblies described above, including the Shrader device, typically form the water cooled crucible in a metallic block, place the emitter mechanism at a distance from the crucible to prevent damage to the emitter, and position permanent or electromagnets to generate a transverse magnetic field to deflect the electron beam and focus it onto the crucible.
The transverse magnetic field used to deflect the electron beam is typically generated between and perpendicular to parallel pole pieces extending from a single magnet, or between spaced, parallel magnets. The transverse magnetic field generally includes substantially uniform field lines between the magnetic pieces, plano-convex field lines above and at the ends of the magnetic pieces, and convex field lines above the plano-convex field lines.
The magnetic structure employed in typical electron gun assemblies generates field lines at the emission site of the electron gun assembly to contain the emitted beam within the assembly and prevent loss or dissipation of the beam therefrom. The beam is typically injected from the emitter into the crucible in the metallic block. Electron beam source assemblies generally are formed integrally with the crucible structure; that is, the crucible is maintained in a fixed position and size relative to the emitter. In some instances, a plurality of crucibles are installed on a rotary table and the crucible containing the material of interest for that step is rotated into position relative to the electron beam source. However, each of these crucibles is typically of the same or at least nearly the same size and, when rotated into position, is the same size and position relative to the emitter as the other crucibles in the turntable.
To vary the size of the crucible has, in the past, required that the entire assembly be redesigned. This limits design flexibility and increases costs for the manufacturer and the user, and increases spare parts costs significantly. However, the arrangement of magnets or electromagnets on either side of the crucible have, in the prior art, made it extremely difficult if not impossible to alter the size of the crucible associated with any given emitter. Conventional designs have limited the industry to what are generally specialized devices for each application.
As a result, there has been a long-felt need in the industry for an electron beam assembly which may be installed with various sizes of crucibles without significant redesign.